Life Can live in the deep Sea
Deep, under the sea floor, with reduced photosynthesis and little organic matter coming from above, the sea floor of the ocean is a marine desert, its life more sparse than in other ocean basins. Photosynthesis is not the only basis for life: locally, methane and hydrogen sulfide seep from the ocean floor, supporting dense oases of organisms that depend on bacteria able to consume these chemicals. Such "chemosynthetic" life does not directly depend on sunlight and can thrive even at great ocean depths. (Aliens of the Deep)
Two basic kinds of “oases” are now known from the oceans. Hot vents, first discovered in 1977, are now known from several places along the Mid-Oceanic Ridge. These seafloor “geysers belch out seawater heated up to 400°C”(Dive and Discover.com) and laden with nutritious chemicals. Dramatic colonies of large clams, giant tubeworms, and other strange life-forms have been discovered at some hot vents.
The second broad category of chemosynthetic oasis is the "cold seep,"* which usually involves the upward seepage of methane dissolved in water or as small bubbles. Mud volcanoes and related cold-seep features form over great sediment accumulations in which bacteria digest buried organic matter, producing methane as a waste product. Specially evolved bacteria oxidize the methane, forming the foundation of a food chain. Different bacteria have evolved to oxidize the foul-smelling hydrogen sulfide, itself the waste product of yet other bacteria living below the ocean floor, which oxidize sulfate ions of seawater origin. The conspicuous and, by bacteria standards, large sulfur bacteria (Beggiatoa spp.) form thin, snow-like mats on the seafloor where seepage takes place. Bacterial mats form at hot vents also, but Beggiatoa is common at cool oceanic seeps and some non-seep environments where hydrogen sulfide rises close to the seafloor and oxygen is present in the water.
Since energy from the sun is the only life people on...